The present invention relates generally to article manipulation, and particularly to manipulation of entire layers of items during palletizing operations.
A pallet is a standard support and carrier structure used in shipping. Pallets provide a support surface receiving items stacked for transport. Pallets include a space below the support surface receiving, for example, the tines of a forklift whereby the forklift lifts and moves the pallet with a stack of items thereon. Typically, items are boxes organized in layers upon the pallet. Efficient shipping of palletized items calls for efficient stacking of items on the pallet to minimize open space within the stack. Furthermore, by varying the orientation and/or pattern of items from layer to layer, a stable stack of items may be constructed upon a pallet. Accordingly, a variety of "box patterns" have emerged for efficient and stable packing together of items in item layers on a pallet. The standard pallet is used widely throughout the shipping industry and a variety of apparatus have evolved in relation to the standard pallet for stacking items upon pallets, i.e., for palletizing.
Thus, palletizing, as used herein, generally refers to a process of constructing a stack of items organized as layers on a pallet. The term palletizing as used herein, however, shall not be limited to stacking relative to a pallet, but shall include generally any stacking process relative to articles organized as stacked layers.
A common arrangement for palletizing uses a rigid planar "apron" to lift from below a layer of items. A layer might be built upon an apron or the apron might be positioned under the layer by sliding the apron between the layer and a supporting surface therebelow. Once positioned below a layer of items, the apron moves and places the item layer elsewhere, e.g., moves the item layer over a pallet or the top layer of a stack of item layers on a pallet. The palletizing device then blocks the layer against movement while the apron slides out from underneath the layer. In this manner, the apron moves and places an entire layer of items upon a pallet or upon the top layer of items on a pallet. Generally, an apron performs only palletizing operations because of the difficulty of inserting an apron between layers of an existing stack of items on a pallet. Unfortunately, use of such a rigid planar apron requires significant space adjacent the pallet stack to accommodate the apron as it is pulled from under the item layer.
One known prior palletizing device, available from the Matthews Conveyor Division, uses a "wrap-around apron" including a set of rollers positioned above a pallet. An item layer is constructed on the rollers and the pallet including any layers stacked thereon moves upward to a point just below the rollers. The item layer is then blocked against movement and the rollers are pulled out from underneath the item layer resting thereon. The item layer thereby drops onto the pallet or stack of item layers resting on the pallet. Unfortunately, this arrangement requires manipulation of the entire pallet and stack of item layers resting on the pallet to position the upper portion thereof just below the rollers and allow a new item layer to come to rest thereon as the rollers are pulled out from thereunder. Accordingly, the rollers follow a path out from underneath the new layer and then down, around, and underneath the entire pallet and stack of items resting thereon. This device is referred to as a "WR Series Palletizer."
U.S. Pat. No. 3,782,564 entitled Product Picking Stacker Crane System, filed Sep. 27, 1971 by Harold S. Burt, shows an overhead crane system transferring item layers from one stack to an adjacent stack. The system is a dual actuator system requiring separate vertical movement actuators and horizontal movement actuators operating in coordination.
U.S. Pat. No. 3,836,018 entitle Discrete Article Palletizing and De-Palletizing apparatus, filed Nov. 5, 1973 by George J. Dawson, et al shows a palletizing device including a top-picking engagement mechanism and a dual actuation drive system, i.e., a horizontal actuation system and a separate vertical actuation system. The illustrated apparatus moves item layers between a first station and a second station.
Thus, article manipulation in the context of palletizing generally requires relatively complex apparatus and associated complex control schemes. Devices using multiple actuators, e.g., gantry systems with x-y positioning of a load, result in relatively complex and expensive apparatus. Because such systems include separate actuation devices operating in different dimensions, e.g., separate devices for movement in an x dimension and a y dimension, such systems can cause abrupt transition in vertical or horizontal movement and thereby risk loss of a load. To avoid such abrupt transition in movement, elaborate coordination and control must be imposed upon the separate actuation devices to accomplish smooth transition in vertical and horizontal movement.
Thus, it would be desirable to provide a palletizing apparatus having a simplified structural architecture and a simplified control scheme for reduced overall cost and reduced overall complexity with a smooth transition in movement of loads.